Interaction Between Zinc, Cadmium, and Lead in Scalp HairSamples of Pakistani and Irish Smokers RheumatoidArthritis Subjects in Relation to Controls

Hassan Imran Afridi & Tasneem Gul Kazi &Dermot Brabazon & Sumsun Naher

Received: 13 November 2011 /Accepted: 27 January 2012 /Published online: 15 February 2012# Springer Science+Business Media, LLC 2012

Abstract The incidence of rheumatoid arthritis (RA) hasbeen associated with cigarette smoking. The aim of our studywas to assess the trace essential and toxic metals, cadmium(Cd), lead (Pb), and zinc (Zn), in scalp hair samples of 32 Irishand 46 Pakistani smokers and non-smokers RA male patientswith age range 42–56 years. For comparison purpose, thescalp hair samples of 27 Irish and 55 Pakistani non-RA malesubjects of the same age group were collected. The concen-trations of trace and toxic elements were measured by induc-tive coupled plasma atomic emission spectrophotometer andatomic absorption spectrophotometer prior to microwave-assisted acid digestion. The validity and accuracy of themethodology was checked using certified reference materialsand using conventional wet acid digestionmethod on the samecertified reference materials (CRMs). The recovery of allstudied elements was found to be in the range of 97.5–99.7% of certified reference values of CRMs. The results ofthis study showed that the mean values of Cd and Pb weresignificantly higher in scalp hair samples of both smoker and

non-smoker RA patients than in referents (P<0.001), whereasthe concentration of Zn was lower in the scalp hair samples ofsmokers and non-smokers rheumatoid arthritis patients. Thedeficiency of Zn and the high exposure of Cd and Pb as aresult of cigarette smoking may be synergistic risk factorsassociated with rheumatoid arthritis.

Keywords Scalp hair . Zinc . Toxic elements . Pakistanirheumatoid arthritis patients . Irish rheumatoid arthritispatients . Atomic absorption spectrophotometer . Inductivelycoupled plasma atomic emission spectrophotometer

Introduction

Rheumatoid arthritis (RA), a systemic skeletal disease char-acterized by a low bone mass, is a major public healthproblem in elderly persons resulting in high incidence offragility fractures, especially hip and vertebral fracture. Inthese people, the high incidence of osteoporotic fracturesleads to considerable mortality, morbidity, reduced mobility,and decreased quality of life [1].

A variety of trace elements are found in bones includingiron, copper (Cu), zinc (Zn), manganese (Mn), fluoride, stron-tium, and boron [2]. Although they are present in only minuteamounts, trace elements influence normal metabolic processesthrough interaction with, or incorporation into, proteins, par-ticularly enzymes [3]. The role of Zn in healthy aging isparticularly important as it prevents neoplastic cell growthand is involved in mitotic cell division, and DNA and RNArepair. Chronic diseases associated with alterations in Znstatus are bronchial asthma and rheumatoid arthritis [4]. Zincplays an important role in nucleic acid synthesis, transcription,and translation as a cofactor for some of the enzymes involvedand may therefore participate in a broad range of metabolic

H. I. Afridi :D. Brabazon : S. NaherMechanical & Manufacturing Engineering,Dublin City University,Dublin, Ireland

D. Brabazone-mail: dermot.brabazon@dcu.ie

S. Nahere-mail: sumsun.naher@dcu.ie

H. I. Afridi (*) : T. G. KaziNational Center of Excellence in Analytical Chemistry,University of Sindh,Jamshoro 76080, Pakistane-mail: hassanimranafridi@yahoo.com

T. G. Kazie-mail: tgkazi@yahoo.com

Biol Trace Elem Res (2012) 148:139–147DOI 10.1007/s12011-012-9352-6

activities in bone. Alkaline phosphate is required for bonecalcification, and collagenase is required for bone resorptionand remodeling [5]. It has been demonstrated that Zn defi-ciency reduces the synthesis and activity of alkaline phosphatein rats [6], and the activity of collagenase in chicks [7]. Zincdeficiency has also been reported to interfere with glycosami-noglycan metabolism of membranous bone and osteoblasticactivity in experimental animals [8]. In addition, Zn has beenshown to stimulate bone formation and to inhibit osteoclasticactivity in vitro [9].

Cigarette design has evolved considerably over the lastfew decades with the incorporation of new tobacco process-es, papers, filters, and several ingredients (flavor, humec-tants, and casing materials), which either alone or incombination have the potential to modify the quantity and/or the quality of the smoke yielded [10]. The tobacco plantabsorbs heavy metals most probably from the soil, fertil-izers, or pesticides [11]. Other environmental factors thatmay influence the uptake of toxic elements by tobaccoplants include the pH of soil, and contaminated irrigatedwater and sewage sludge used as fertilizers. Tobacco smok-ing delivers 87 organic carcinogens to the lungs, in additionto toxic elements [12], which may partition into the smokephase on combustion [12]. Some of these [cadmium (Cd),nickel (Ni), and lead (Pb)] readily pass into the bloodstreamand may accumulate in specific organs, such as the kidneyand liver [13]. There are a few studies that have reported onthe large variations of toxic elements in the compositions ofcommercial tobacco products, which have tried to linksmoking-related diseases with toxic elements derived fromtobacco combustion [14]. The intake of trace and toxicelements may promote rheumatoid arthritis disorders byincreasing oxidative stress (for example, by catalyzing theproduction of reactive oxygen species or inhibiting theirdegradation) due to the deficiency of antioxidant elements(Zn, Cu, and Mn). The deficiency of essential nutrients, lackof homeostatic control, or an excess intake of some toxicelements causes chronic physiological disorders, such ashypertension, cardiovascular disease, and rheumatoidarthritis [15].

Determinations of trace elements in human tissues andfluids were used to obtain information on nutritional statusfor diagnosis of diseases, indication of systemic intoxica-tion, and to obtain information on environmental exposure.In the majority of cases, whole blood, serum, plasma, andurine were analyzed [16]. Hair can provide a more perma-nent record of trace and toxic elements associated withnormal and abnormal metabolism as well as toxic elementsassimilated from the environment. In addition, hair is easilycollected, conveniently stored, and easily treated. Therefore,the analysis of human hair has become an important way tounderstand any quantitative change in certain elements in-side the body [17].

One of the most widely used analytical techniques for thedetermination of different elements in biological and environ-mental materials are atomic absorption spectrometry and in-ductively coupled plasma atomic emission spectrometry dueto its advantages over other analytical techniques [18]. Themineralization method is most frequently applied for the anal-ysis of biological samples or wet digestion with concentratedacids using either conventional heating or microwave energyfor oxidizing the organic matter [16]. The main advantage ofmicrowave-assisted samples pretreatment is its requirement ofsmall amount of mineral acids and a reduction in the produc-tion of nitrous vapors. Microwave systems keep blank levelslow because only small volumes of reagents are required andallow more samples to be processed per hour than conven-tional digestion systems [19].

The aim and objective of our present study was to assessthe concentrations of Cd, Pb, and Zn in the scalp hairsamples of Pakistani and Irish male smoker rheumatoidarthritis patients. For a comparative study, 27 Irish and 55Pakistani non-rheumatoid arthritis individuals (smoker andnon-smokers) of the same age group (range 42–56 years),socioeconomic status, localities, and dietary habits wereselected as referents. The metal levels were also examinedfor a possible mutual correlation and were compared withreported metal levels for donors from other regions of theworld. It was anticipated that the comparative metal levels inhair of Pakistani and Irish referent segments would bring outdistinct sources responsible for the distribution of selectedmetals to help assess the nutritional status and environmen-tal exposure of the two categories of subjects compared withthose from other nations where different environmental andliving conditions prevail.

Materials and Methods

Apparatus

The analysis of elements in Ireland was carried out by meansof a Varian Liberty 220 (Mulgrave, Victoria, Australia) Induc-tively Coupled Plasma Atomic Emission Spectrometer usingthe axially viewed plasma. The Liberty Series II ICP features a40-MHz free running RF generator and a 0.75-m Czerny–Turner monochromator with 1,800 grooves/mm holographicgrating used in up to four orders. The resolution of the spec-trometer is typically 0.018 nm in first order, 0.009 nm insecond order, 0.007 nm in third order, and 0.006 nm in fourthorder. The instrument was controlled with a Digital Equip-ment Corporation (DEC) Venturis computer with an IntelPentium processor and Varian Plasma 96 software runningunder Microsoft Windows 95 operating system. The instru-mental conditions are shown in Tables 1 and 2. A Hinari Lifestyle (Elstree, Hertfordshire, UK) domestic microwave oven

140 Afridi et al.

(maximum heating power of 800W) was used for digestion ofthe scalp hair samples.

The analysis of elements in Pakistan was carried out bymeans of a double beam Perkin-Elmer atomic absorptionspectrometer model 700 (Norwalk, CT, USA) equipped witha flame burner and graphite furnace HGA-400, a pyrocoatedgraphite tube with an integrated platform, and an autosam-pler AS-800 (Perkin Elmer). The instrumental parametersare shown in Table 3. Zn was measured under optimizedoperating conditions using FAAS with an air–acetyleneflame, whereas Cd and Pb were determined using ETAAS.Signals were measured as absorbance peaks in the flameabsorption mode, whereas integrated absorbance values(peak area) were determined in the graphite furnace. A Pel(PMO23, Osaka, Japan) domestic microwave oven (maxi-mum heating power of 900 W) was used for digestion of thescalp hair samples. Acid-washed PTFE (polytetrafluoro-ethylene) vessels (Kartell, Milan, Italy) and flasks were usedfor preparing and storing solutions.

Reagents and Glasswares

Ultrapure water obtained from ELGA Lab Water system(Bucks, UK) was used throughout the work. Concentratednitric acid (65%) and hydrogen peroxide (30%) wereobtained from Merck (Darmstadt, Germany) and checkedfor possible trace metal contamination. Working standardsolutions of Cd, Pb, and Zn were prepared immediatelyprior to their use, by stepwise dilution of certified standardsolutions (1,000 ppm) Fluka Kamica (Buchs, Switzerland),with 0.5 M HNO3. All solutions were stored in polyethylene

bottles at 4°C. For the accuracy of methodology, the certi-fied reference materials (CRMs), human hair NCSZN81002b (Beijing, China), and certified reference materials(CRMs) of human hair BCR 397 (Brussels, Belgium) wereused (Table 4). All glassware and plastic materials usedwere previously soaked for 24 h in 5 M nitric acid, washedwith distilled water and finally rinsed with ultrapure water,dried, and stored in class 100 laminar flow hoods.

Sample Collection and Pretreatment

This study was completed in two phases. Phase 1 wascompleted during January 2005 to June 2006 and phase 2during July 2010 to October 2010. The sampling locationswere Hyderabad, Pakistan and Dublin, Ireland. The donorages of both countries ranged between 42 and 56 years fromeach location. Before the start of this study, all referents andrheumatoid arthritis patients of both countries were in-formed through a consent form by the administration aboutthe aim of study, and all agreed to participate and signed theform. A questionnaire was also administered to them tocollect details regarding physical data, ethnic origin, health,duration and frequency of smoking, dietary habits, age, andconsent. The RA patients were grouped according to theirhabits—non-smokers (NSRA) and smokers (SRA). Whilecontrol groups were also divided into two groups, referentnon-smokers (RNS) and smokers (RS) are shown in Table 5.All the patients had active disease defined by the followingcriteria: erythrocyte sedimentation rate (ESR) of at least30 mm/h, six or more tender joints, three or more swollenjoints, and morning stiffness of at least 30-min duration.Thirty Irish and 37 Pakistani patients had IgM-positiverheumatoid factor. None of the patients had been treatedwith steroids, immunosuppressives, or penicillamine withinthe 3 months before the study. They all were receiving non-steroidal anti-inflammatory drugs (NSAIDs) (diclofenac so-dium, 100 mg/day).

Physical examinations were carried out in a basic healthunit of Hyderabad, Pakistan and Dublin, Ireland to measure

Table 1 Measurement conditions for inductive coupled plasma atomicemission spectroscopy Liberty 220 ICP-AES

Parameters Cd Pb Zn

Wavelength (nm) 226.502 220.553 213.8

Height (mm) 3 3 5

Windows (nm) (abovethe coil)

0.027 0.027 0.027

Scan (nm) 0.040 0.040 0.040

Integration (s) 3 3 3

Replicates 3 3 3

Sample uptake (s) 30 30 30

PMT (V) 650 650 650

Power (kW) 1.10 1.10 1.10

Plasma flow (l/min) 15.0 15.0 15.0

Auxiliary flow (l/min) 1.50 1.50 1.50

Pump speed (rpm) 15 15 15

Background mode Dynamic Dynamic Dynamic

Max curve order 1 1 1

C.C. limit 0.995 0.995 0.995

Table 2 Liberty 220common parameters Nebulizer type V-groove

Nebulizerpressure

150 kPa

Stabilization time 10 s

Sample delaytime

30 s

Rinse time 10 s

Pump–tube Orange–orange(inlet)

Blue–blue (outlet)

Snout purge Off

Fast pump On

Correlation of Essential Trace and Toxic Elements with Rheumatoid Arthritis 141

participant’s weight, height, blood pressure, and biochemi-cal data. For all patients and referents, anthropometricparameters including weight, height, and waist circumfer-ence were measured using the standard protocols. Therewere no statistically significant differences between bothgroups of patients and referents with regard to height andweight. The study protocol was approved by the local ethicscommittee of higher education commission, Islamabad,Pakistan. The criteria of healthy subjects included no historyof symptoms of any related disease to arthritis documentedin their medical notes. All control subjects underwent aroutine medical examination. The dietary habits of Pakistanipeople (elder age group) depend upon animals (chicken,mutton, beef) and plants (vegetables, beans and grain) whilethe Irish people used chicken, vegetables, and beans.

Collection of Scalp Hair Samples

The hair samples (~1.0 g each) were taken from the nape ofthe neck. Hair samples were put into separate plastic enve-lopes for each participant on which the identification (ID)number of the participant was indicated. The plastic enve-lope of each subject was tightly sealed and attached to a

questionnaire. Before analysis, each individual hair samplewas cut into approximately 0.5-cm-long pieces and mixed toallow a representative subsampling of the hair specimen.After cutting, each sample was washed with diluted TritonX-100; samples were then rinsed with distilled water andthen with deionized water. The samples were rinsed threetimes with acetone [19]. All samples were then dried in anoven at 75±5°C for 2 h. Dried samples were stored sepa-rately in polyethylene bags.

Microwave-Assisted Acid Digestion (MWD)

Duplicate samples of scalp hair (200 mg) of each RApatients and control individuals were directly placed intoTeflon PFA flasks. Two milliliters of a freshly preparedmixture of concentrated HNO3–H2O2 (2:1, v/v) was addedto each flask and kept for 10 min at room temperature thenplaced in a covered PTFE container. This was then heatedfollowing a one-stage digestion program at 80% of totalpower (800 W). Complete digestion of scalp hair samplesrequired 5–8 min. After the digestion, the flasks were left tocool and the resulting solution was evaporated to semidriedmass to remove excess acid. About 5 ml of 0.1 M nitric acid

Table 3 Measurement condi-tions for elements using flameand electrothermal atomic ab-sorption spectrometry

Sample volume010 μl,cuvette0cup, carrier gas0200 ml/min. Background cor-rection (D2 lamp) used for allelements

Parameters Cd Pb Zn

Lamp current (MA) 6.0 8.0 7.5

Wavelength (nm) 228.8 283.3 213.8

Slit width (nm) 0.7 0.7 0.7

Dry temperature (°C)/ramp/hold (s) 140/15/5 140/15/5 Burner height07.5 mm

Ashing temperature (°C)/ramp/hold (s) 850/10/20 700/10/20 Oxidant (air)017.0 lmin−1

Atomization temperature (°C)/ramp/hold(s)

1,650/0/5.0 1,800/0/5.0

Fuel (acetylene)02.0 lmin−1

Cleaning temperature (°C)/ramp/hold (s) 2,600/1/3 2,600/1/3

Chemical modifier Mg(NO3)2+Pd(NO3)2

Mg(NO3)2

Table 4 Determination of trace elements in certified sample of human hair (CRM) by conventional (CDM) and microwave digestion method(MWD) (n010)

Elements Conventional digestion method CDM Microwave digestion method MWD T valuea % recoveryb Certified values

Certified human hair reference material (NCS ZC 81002b) (μg/g)

Cd 0.0716±0.003 (4.19) 0.0714±0.006 (8.40) 0.305 99.7 0.072±0.010

Pb 3.80±0.37 (9.74) 3.72±0.35 (9.41) 0.081 98.05 3.83±0.18

Zn 191±7.28 (3.81) 187±9.53 (5.09) 0.648 97.9 191±16

Certified human hair material CRM 397 (μg/g)

Cd 0.53±0.025 (4.72) 0.524±0.024 (4.58) 0.2256 98.87 0.52±0.024

Pb 33.29±1.21 (3.63) 32.56±1.18 (3.62) 0.096 97.8 33±1.2

Zn 197±12.8 (6.2) 194±11.3 (5.7) 0.0345 98.6 199±5

a Paired t test between CDM and MWD, df09, T (critical) at 95% CI02.262, P00.05. Means in percentage. Values in parentheses are RSDb% recovery was calculated according to the following: MDM½ �

CDM½ � � 100

142 Afridi et al.

was added to the residue and filtered through a Whatman no.42 filter paper and diluted with deionized water up to10.0 ml in volumetric flasks. Blank extractions were carriedthrough the complete procedure. Blanks and standard sol-utions were prepared in a similar acid matrix. The validityand efficiency of the MWD method was checked withcertified values of human hair NCSZC 81002b and certifiedhuman hair CRM 397 and with those obtained from con-ventional wet acid digestion method [17].

Analytical Figures of Merit

Statistical analyses were performed using computer programExcel XL State (Microsoft Corp., Redmond, WA, USA) andMinitab 13.2 (Minitab Inc., State College, PA, USA). Cal-ibration was performed with a series of Cd, Pb, and Znstandards. Sensitivity (m) was the slope value obtained byleast-square regression analysis of calibration curves basedon peak areameasurements. The linear range of the calibrationcurve ranged from the quantification limit up to 100 μg/l wasused for all trace and toxic elements.

Results

The concentrations of Zn in the scalp hair samples of Irishmale referent non-smokers (RNS) and referent smokers(RS) were significantly higher at 95% confidence interval(CI) (196–207) and (175–182) μg/g, respectively, than those

values observed for rheumatoid arthritis non-smokers(RANS) and rheumatoid arthritis smokers patients (RAS)(CI0131–140 and CI0120–124 μg/g, respectively, withP<0.001). In Pakistani subjects, Zn levels in the scalp hairsamples of RANS and RAS (CI0130–146 and CI0106–118 μg/g, respectively) were found to be lower than those inRNS and RS (CI0239–258 and CI0216–233 μg/g, respec-tively, P<0.001) (Table 6).

An elevated level of Cd content was observed in the scalphair of Irish RANS and RAS. The ranges of Cd in the scalphair samples of RNS and RS were CI 0.64–0.73 and CI0.87–1.00 μg/g, respectively, whereas those in RANS andRAS were CI 1.98–2.32 μg/g and CI 3.06–3.68 μg/g, re-spectively (P<0.001). The same trend was observed inPakistani subjects (Table 6). The Pb concentration in thescalp hair samples of Irish RAS was found in the range of CI3.15–3.56 μg/g, whereas in the RANS, the Pb level was inthe range of CI 4.38–4.71 μg/g (Table 6). Similarly, a higherlevel of Pb was observed in RAS (CI 5.22–6.08 μg/g) thanin RS (P<0.001). The same trend was observed in Pakistanisubjects (Table 6).

It was observed that the levels of all three elements weresignificantly higher in scalp hair samples of Pakistani pop-ulation as compared to Irish subjects of same age group(P00.01–0.001).

Discussion

The present study brings out data related to the metal distribu-tion in hair with related to arthritis disease and smoking habitsin two different countries. Table 6 presents the concentration ofessential trace and toxic elements (Zn, Cd, and Pb) in scalp hairsamples of Irish and Pakistani RA and referent donors.

Rheumatoid arthritis is an autoimmune disease, a disor-der in which the body attacks its own healthy cells andtissues. The result shows that the level of Zn in scalp hairsamples of smokers and non-smokers RA patients was low-er than referents (Table 6). Zn deficiency is associated with

Table 5 The number of subjects as control and rheumatoid arthritispatients of age group 42–56 years

Countries Referents Rheumatoid arthritis

Smokers Non-smokers Smokers Non-smokers

Pakistan 47 52 39 34

Ireland 22 19 23 20

Table 6 Concentrations of traceand toxic metals in scalp hairsamples of Irish and Pakistanimale smokers and non-smokersreferent and rheumatoid arthritis(RA) subjects (μg/g)

Elements Non-smokers Smokers

Referents Rheumatoid arthritis P value Referents Rheumatoid arthritis P value

Irish subjects

Cadmium 0.68±0.07 2.13±0.37 0.001 0.94±0.12 3.35±0.61 0.001

Lead 3.36±0.41 4.55±0.34 0.009 3.75±0.28 5.62±0.87 0.003

Zinc 203±7.53 135±9.42 0.001 178±5.28 122±4.63 0.001

Pakistani subjects

Cadmium 1.55±0.42 4.59±0.51 0.001 2.38±0.29 5.86±0.63 0.001

Lead 5.79±0.74 9.34±0.72 0.003 6.82±0.65 11.6±1.05 0.002

Zinc 250±19.3 138±16.5 0.001 225±17.1 112±9.67 0.001

Correlation of Essential Trace and Toxic Elements with Rheumatoid Arthritis 143

delayed bone growth, but few studies have been done toelucidate its potential role in bone turnover regulation. Theskeleton is a major bone store of Zn, and in humans approx-imately 30% of total body Zn is found in bone, probablybound to hydroxyapatite [20]. It has been proposed thatsince urinary Zn excretion is almost uninfluenced by varia-tion in diet, urinary Zn excretion may be used as a marker ofchanges in bone metabolism [21]. Zinc supplementationwas reported to decrease periarticular osteoporosis in RApatients [22]. Defects in skeletal development have beenreported in man due to Zn deficiency and also due to theacrodermatitis enteropathica, an inherited congenital disor-der of Zn absorption [23]. It has been reported that forearmbone mineral content is correlated with Zn intake in pre-menopausal women, suggesting a possible role of Zn in themaintenance of bone mass [24]. It was reported in literaturethat amino acid complex of Zn (β-alanyl-L-histidinato zinc)has more potent effect than Zn sulfate on bone metabolismin experimental animals, and this Zn chelate has been pro-posed as a possible treatment for osteoporosis [25, 26].

The mean levels of Pb and Cd in the scalp hair samples ofnon-smoker referents of both countries were found to belower than those recorded in smokers and non-smokers RApatients (Table 6). Pb has an exceptionally long half-life inbone (more than 20 years) compared to other elements (Cu,Fe, Zn) [27]; it is not the only metal which can deposit inbone from respiratory exposure. Other metals which canaccumulate in bone as a result of respiratory exposure in-clude arsenic, Cd, cobalt, and antimony [27]. Pb can in-crease osteoporosis and it may disrupt the normal formationof Ca hydroxyapatite, thus critically weakening the bone[28]. Tandon et al. [4] in his study noted that the effects ofPb on humans include anemia, abdominal colic, and gumwastage, while Cd alters calcium (Ca) and phosphorus me-tabolism, thus contributing to arthritis, osteoporosis, andneuromuscular diseases. Toxic elements (Cd, Pb, and Ni)may deplete glutathione and protein-bound sulfhydrylgroups, resulting in the production of reactive oxygen spe-cies, such as superoxide anion, hydrogen peroxide, andhydroxyl radical [29].

Tobacco leaves naturally accumulate and concentraterelatively high levels of Cu (7.1–68.8), Cd (5.73–7.96), Pb(0.04–14.4), and Ni (2.21–3.45) as compared to medicinaland edible plants Cu (0.686–0.953), Cd (0.072–0.12), Pb(0.374–0.615), and Ni (0.31–0.523) [30, 31]; therefore,smoking of tobacco is an important source of these metalsexposure for smokers [32]. The total amount of carcinogensin cigarette smoke ranges from 1 to 3 μg per cigarette [13].The country of origin and type of the product play majorroles in determining the chemical composition of cigarettetobacco [32]. It was investigated that one pack of cigarettesdeposits 2–4 μg Cd, 1–2 μg Pb, and 0.96–1.34 μg Ni intothe lungs of a smoker, whereas some of the smoke passes

into the air to be inhaled by smokers and non-smokers alike[33, 34]. It was also consistent with another study thatsmokers generally exhibit significantly higher Cd, Ni, andPb body burdens than non-smokers [32]. The results sug-gested that although these toxic elements (Cd, Ni, Pb) pose ahazard to essential trace metal homeostasis of variousorgans, co-exposure can pose a major threat, while con-sumption of ethanol may absorb much more Cd and Pb thantheir unexposed counterparts [35].

In the past few years, increasing consideration has beengiven to interactions occurring in the organism betweentoxic metals and bioelements essential for life. These inter-actions are complex and involve biometals such as Zn, Cu,Fe, Se, Ca, and toxic elements, including Cd [36]. The basisof Cd toxicity is its negative influence on enzymatic systemsof cells, resulting from substitution of other essential metalions (mainly Zn, Cu, and Ca) in metalloenzymes and itsvery strong affinity to biological structures containing –SHgroups, such as proteins, enzymes, and nucleic acids [37].The relevance of Cd and Pb–Zn interactions should beconsidered in the light of the general population exposureto toxic metals [38] and common deficiency of Zn in theworld, mainly due to nutritional factors [39].

This is the first study with comprehensive data on toxicand essential elements in the scalp hair samples of malerheumatoid arthritis and referent smokers and non-smokerssubjects of two countries (Pakistan and Ireland). The con-centrations of essential trace and toxic elements in scalp hairsamples of the Irish referent subjects were close to thosereported from other European [36–42], American [43–45],and Australian [46] countries (Table 7). The elemental con-centrations of Cd and Pb in Pakistani referents were almosthigher than in European countries, which are in agreementwith the studies carried out in Asian [2, 47–59] and Africancountries [60–64] (Table 7).

Humans are also affected by Cd through smoking andconsumption of foods and beverages. Rice is the mainsource of Cd in rice-eating countries. Human Pb exposureis mainly through air and food. In most developed countries,the fuel content of Pb has been controlled but still remainsan issue of immediate consideration in developing countries,including Pakistan. Other sources of Pb exposure includePb-based paints, Pb pipelines in water supply systems, andceramics. The Pb-based products, including paints and foodcontainers, are not completely banned in Pakistan [65].

Conclusion

It can be concluded that impaired trace element metabolismof the essential trace and toxic elements may have a role inthe pathogenesis and progression of arthritis. The reallyoverlooked issue here is the dramatic impact of the toxic

144 Afridi et al.

metals on human health. Commonly, when the body burdenof these metals is in excess, the symptoms manifest in theform of muscle and joint complaints. This is because heavymetals interfere with the normal biochemical processes in-volving Zn and other nutrients in the cells of human body.When these essential minerals in the body are disrupted byheavy metals, musculoskeletal symptoms such as muscle

Table 7 Comparison of different elemental contents (μg/g) in scalphair of people from various parts of the world

Authors Elements Age(years)

N x±s (μg/g)

Europe

Sweden

Rodushkin andAxelsson [40]

Pb 1–75 114 0.22–7.26

Cd 1–75 114 0.010–0.356

Zn 1–75 114 68–198

Poland

Nowak andChmielnicka [41]

Pb 25–39 624 4.8–5.7

Cd 25–39 624 0.56±2.3

Zn 25–39 624 132.7±135.7

Trojanowskiet al. [42]

Pb 26–50 109 3.71±0.29

Cd 109 0.401±0.035

Pb 51–75 121 3.88±0.35

Cd 121 0.260±0.022

Italy

Sturaro et al. [43] Zn 21–60 50 171–314

Pb 21–60 50 6.5–8.7

France

Goulle et al. [44] Zn 40–60 45 129–209

Pb 40–60 45 0.13–4.57

Netherlands

Iyengar andWolttlez [45]

Zn 21–60 50 176±38

South America

Nagra et al. [46] Cd 22–59 50 31.6±38

North America

Saiki et al. [47] Zn 50–70 50 45–162

Zn 71–87 50 30–202

Australia

McKenzie [48] Zn 16–56 118 189±24

Asia

Pakistan

Pasha et al. [49] Pb 15–94 86 14.62±8.01(0.577–31.8)

Cd 15–94 86 2.13±1.74(0.196–9.17)

Zn 15–94 86 154.2±117.1(12.4–729.2)

Pasha et al. [50] Pb 37–65 37 15.50±8.11

Cd 37–65 37 1.675±1.13

Zn 37–65 37 140.7±79.5

Shah et al. [51]

(Pak) Pb 3–54 62 15.97±5.56

(Lib) 3–54 62 24.95±8.69

(Pak) Cd 3–54 62 0.38±0.186

(Lib) 3–54 62 0.53±0.26

(Pak) Zn 3–54 62 226±53.7

(Lib) 3–54 62 190±34.0

Khalique et al. [52] Cd 41–50 18 0.300±0.140

Table 7 (continued)

Authors Elements Age(years)

N x±s (μg/g)

Zn 41–50 18 270±46.5

India

Vishwanathanet al. [53]

Pb 36±1.23 25 24.8±5.92

Cd 36±1.23 25 5.12±3.41

Zn 36±1.23 25 265.2±17.3

Sukumar andSubramanian[54]

Pb 31–45 17 8.9±1.9

46–60 11 4.5±2.8

Cd 31–45 17 1.5±0.3

46–60 11 1.9±0.5

Zn 31–45 17 87.0±1.9

46–60 11 112.8±25.3

Mehra andJuneja [55]

Pb 1–30 50 7.60±6.44

Cd 1–30 50 0.32±0.21

Zn 1–30 50 182.4±45.2

Rao et al. [56] Cd 17–60 20 0.12–0.61

Zn 17–60 20 45.44–123.5

Pb 17–60 20 0.75–4.1

Turkey

Sasmaz et al. [57] Pb – 26 3.06±1.42

Cd – 26 0.67±0.33

Ulvi et al. [58] Zn 47.76±13.11 29 176.96

Hong Kong

Man and Zheng [59] Pb 20–50 30 12.04±7.0

Zn 20–50 30 184.85±60.89

Man et al. [60] Zn 30–69 95 355–503

Africa

Nigeria

Nnorom et al. [61] Pb 1–30 46 63.6

Cd 1–30 46 1.0

Zn 1–30 46 128.6

Syria

Khuder et al. [62] Pb 21–59 281 10.7±8.9

Zn 21–59 281 260±113

Sudan

Eltayeb andVan-Grieken [63]

Zn 30–50 35 89–170

Pb 30–50 35 3–17

Egypt

Mortadaet al. [64]

Pb 28–40 93 1.8–9.7

Cd 28–40 93 0.08–0.82

Correlation of Essential Trace and Toxic Elements with Rheumatoid Arthritis 145

and joint pain commonly occur. These toxic metals impairthe immune system, cause abnormal cell responses, and mayaggravate our sign and symptom of arthritis disorders. It isnecessary to add these minerals via food supplements. Theresults of this study provided guidance to clinicians andother professional investigating deficiency of essential tracemetals and excessive level of toxic metals in biologicalsamples of healthy and arthritis patients. This study alsoprovides some support for the hypothesis that dietary intakeor inhalation of toxic elements (Cd and Pb), most probablythrough smoking cigarette, may increase the risk of rheu-matoid arthritis and related disorders, which indicates thatthe causal link may be stronger among cigarette smokers.We propose that essential and toxic elemental measurementsmay be performed on patients reaching in the emergencydepartment to test whether its concentration may serve notonly as markers of rheumatoid arthritis and its remedies butalso as predictors of adverse outcomes.

Acknowledgment Dr. Hassan Imran Afridi is grateful to HigherEducation Commission (HEC) of Pakistan for providing the scholar-ships for the post-doctoral research work. Dr. H.I. Afridi is alsothankful to National Center of Excellence in Analytical Chemistry,University of Sindh, Jamshoro, Pakistan for the grant of sabbaticalleave.

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